The proposed research will investigate the occurrence of multiple sites of spontaneous spiking and the spread of excitation in vascular muscle. Glass pore electrodes will be used to extracellularly record simultaneously from several points on hepatic portal vein, and other vessels, during spontaneous and induced spiking in solutions with varying ionic composition and nerve blocking agents, such as tetrodotoxin. The importance of neural factors and other factors influencing excitability of the muscle cell will then be assessed. Hypertonicity will be used to alter the degree of cell contact and changes in spread of electrical activity will be determined. Microdissection of blood vessel strips will be carried out to find out whether there is a relationship between conduction velocity and bundle size, and whether there is a minimum bundle size necessary for conduction to occur. Cell culture of vascular muscle will be used to determine the influence of the number of cells in an aggregate on membrane properties. Simultaneous use of two intracellular microelectrodes in Wheatstone bridge circuits will allow measurement of cell-to-cell coupling of electrotonic pulses and elucidate and any directionality of conduction. Injection of sinusoidal currents over a range of frequencies in such a two-microelectrode apparatus may allow characterization of the impedance properties of cell junctions. Cell culture preparations will be observed with the differential interference contrast (Nomarski) optical method to exactly define the geometry of the cells being used. Procion dye will be injected into vascular muscle to determine whether it can cross cell junctions thought to be electrically coupled. Cell junctions will be studied by electron microscopy to determine the correlation between ultrastructural features and electrical behavior, and the concurrence of changes in structure and function imposed by changes in bathing solutions, such as hypertonicity or low Ca ions.